Jest upgrade from v26 to v29

Jest upgrade to v27 was required to resolve word-wrap ReDoS vulnerability, multiple MFEs are already on v29 and some on v28, we decided to update jest to latest version which is v29, across all MFEs. Following are the details of breaking changes between each version

Jest v27 Upgrade (Complete changelog)

Introduced a few more small breaking changes to help you avoid mistakes by disallowing some things that can easily happen unintentionally:

  • The same done test callback may not be called more than once,

  • calling done and returning a Promise may not be combined,

  • a describe block must not return anything,

and we made some TypeScript types stricter.

Modules used in the following configuration options are now transformed like the rest of your code, which may be breaking if you relied on them being loaded as-is:

  • testEnvironment

  • runner

  • testRunner

  • snapshotResolver


Jest v28 Upgrade (Complete changelog)

The supported Node versions are 12.13, 14.15, 16.10 and above.


Configuration Options:

  • extraGlobals: The extraGlobals option was renamed to sandboxInjectedGlobals:

  • timers: The timers option was renamed to fakeTimers

  • testURL: The testURL option is removed. Now you should use testEnvironmentOptions to pass url option to JSDOM environment

  • Babel Config: babel-jest now passes root: config.rootDir to Babel when resolving configuration.

  • expect: In versions prior to Jest 28, toHaveProperty checked for equality instead of existence, which means that e.g. expect({}).toHaveProperty('a', undefined) is a passing test. This has been changed in Jest 28 to fail. Additionally, if you import expect directly, it has been changed from default export to a named export


Fake Timers:

Fake timers were refactored to allow passing options to the underlying @sinonjs/fake-timers

  • fakeTimers: The timers configuration option was renamed to fakeTimers and now takes an object with options

  • jest.useFakeTimers(): An object with options now should be passed to jest.useFakeTimers() as well


Test Environment:

  • Custom Environment: The constructor of test environment class now receives an object with Jest's globalConfig and projectConfig as its first argument. The second argument is now mandatory. In addition, test environments are now exported with the name TestEnvironment, instead of simply exporting the class directly:

  • jsdom: If you are using JSDOM test environment, jest-environment-jsdom package now must be installed separately


Test Runner: When using Jasmine test runner, jest-jasmine2 package now must be installed separately.


Transformer: process() and processAsync() methods of a custom transformer module cannot return a string anymore. They must always return an object.



  • jest.fn(): now takes only one generic type argument


Jest v29 Upgrade (Complete changelog)

The supported Node versions are 14.15, 16.10, 18.0 and above. v29 introduces following breaking changes

  • Snapshot format: Jest 29 has changed the default snapshot formatting to {escapeString: false, printBasicPrototype: false}

  • JSDOM upgrade: jest-environment-jsdom has upgraded jsdom from v19 to v20. If you use jest-environment-jsdom, the minimum TypeScript version is set to 4.5. Notably, jsdom@20 includes support for crypto.getRandomValues(), which means packages like uuid and nanoid, which doesn't work properly in Jest@28, can work without extra polyfills.

  • pretty-format​: ConvertAnsi plugin is removed from pretty-format package in favour of jest-serializer-ansi-escapes.

  • jest-mock: Exports of Mocked* utility types from jest-mock package have changed. MaybeMockedDeep and MaybeMocked now are exported as Mocked and MockedShallow respectively; only deep mocked variants of MockedClass, MockedFunction and MockedObject are exposed.

  • jest.mocked(): The jest.mocked() helper method now wraps types of deep members of passed object by default. If you have used the method with true as the second argument, remove it to avoid type errors